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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Mechanically-, Thermally, and Chemically-Robust High-Temperature Ceramic Composites

In an effort to lower the levelized cost of electricity generated by Concentrated Solar Power (CSP) plants, the heat-to-electricity conversion efficiency may be increased by operating such plants with higher turbine inlet temperatures using closed Brayton cycles with high-pressure, supercritical carbon dioxide (sCO 2 ) as the working fluid. For example, if the turbine inlet temperature is raised to ≥750°C, in combination with sCO2 closed Brayton cycles, the relative heat-to-electricity efficiency may be raised by more than 20% (compared to subcritical steam Rankine cycles operating with turbine inlet temperatures ≤550°C). The associated reduction in the cost of dispatchable electricity from such CSP plants (utilizing high-temperature thermal energy storage) would be an important breakthrough on the path towards direct competition with fossil-fuel-based plants. A key barrier to achieve such high-temperature efficient operation has been the limited thermomechanical performance of metal alloys used in compact, primary printed circuit- type heat exchangers (PCHEXs) for heat transfer to high-pressure sCO 2 . The maximum allowed stresses for the use of conventional stainless steels and nickel-based superalloys at high sCO 2 pressures (≥20 MPa) decline rapidly at temperatures ≥550°C. This project has been focused on demonstrating the desired high-temperature properties and attractive manufacturing characteristics of mechanically-, thermally-, and chemically-robust ceramic/metal composites (cermets), in order to allow for the use of such composites in primary PCHEXs for heat transfer to sCO 2 at ≥750°C and ≥20 MPa in CSP plants. Prior work with high-temperature, co-continuous carbide/refractory metal cermets, such as ZrC/W composites, has already demonstrated: i) the attractive combination of high-temperature properties exhibited by such materials (e.g., high values of stiffness, failure strength, and thermal conductivity at 800°C), and ii) cost-effective processes for manufacturing PCHEX plates comprised of such cermets with tailorable channel patterns. However, ZrC/W cermets were not found to be inherently corrosion resistant in sCO 2 at 750°C and 20 MPa. While the application of a Cu coating to ZrC/W surfaces, along with a modest addition (50 ppm) of CO to CO 2 , rendered such composites resistant to corrosion for 1000 h in such sCO 2 -based fluids at 750°C, such additional steps would increase the design complexity of such cermet-based components. An alternative approach (the focus of this project) is to develop mechanically-robust, cost- effective cermets that are inherently resistant to high-temperature oxidation in air and CO 2 . The overall goals of this project have been to demonstrate: i) the oxidation resistance of at least one cermet at 750°C in air and in CO 2 (i.e., with a projected annual corrosion ≤30 μm), ii) the mechanically robust nature of at least one cermet at 750°C (i.e., with an average failure strength ≥200 MPa), and iii) that the selected cermet can be manufactured via low-cost forming techniques.

14 SOLAR ENERGY↗
DOE OSTI2026

Development of a Test-Bed for Testing and Refining EarthEn’s Supercritical CO 2 Based Energy Storage System

EarthEn’s energy storage concept leverages supercritical carbon dioxide (sCO 2 ) as a working fluid and relies on compact, high-performance components operating at elevated pressures and temperatures. To accelerate component development and reduce technical risk prior to larger-scale demonstrations, Oak Ridge National Laboratory (ORNL) developed a 100 kW-scale sCO 2 test-bed under a Cooperative Research and Development Agreement with EarthEn (CRADA NO. NFE-24-10050). The objective of the work was to design and construct a flexible experimental facility capable of reproducing key thermodynamic state points and heat-transfer conditions relevant to EarthEn’s thermal energy storage (TES) cycle, with particular emphasis on enabling development and evaluation of next-generation heat exchangers and TES concepts. The test-bed consists of a closed-loop sCO 2 circulation system housed within an open-topped enclosure. In its as-installed configuration, dense-phase sCO 2 is recirculated through a printed circuit recuperator, an electrically heated section, a throttling device used to simulate turbine expansion, and a water-cooled printed circuit heat exchanger that rejects heat to the building chilled-water system before returning to the pump. The pump is driven by a variable frequency drive, enabling controlled adjustment of flow and operating point. A comprehensive instrumentation suite was integrated to support both safe operation and high-quality data collection. Installed sensors include Coriolis flow meters for sCO 2 flow rate and density, resistance temperature detectors and thermocouples distributed throughout the loop (including the heated section and key heat exchanger ports), and pressure transducers for absolute and differential pressure measurements. The facility was designed to support high-pressure (19 MPa nominal) and high-temperature (575°C nominal) operation with credited overpressure protection provided by a rupture disk. Nominal operating conditions were selected to support 100 kW-class testing while maintaining flexibility for non-heated and heated shakedown, control development, and future integration of advanced TES test sections. In parallel with facility development, a system-level thermal-hydraulic model was created using Modelica-based tools to support component sizing, anticipate performance over targeted test conditions, and establish a framework for future model calibration against experimental data. At the conclusion of the project performance period, the facility was in final assembly, and the pressure boundary was nearly completed. However, several practical challenges associated with high-pressure/high-temperature systems and specialized component procurement impacted schedule and prevented initial pump-driven operation and full commissioning within the available resources. This report documents the as-built design, operating capabilities, and instrumentation, and it summarizes key lessons learned related to heater fabrication and testing, first-of-a-kind assembly factors, specialty flange supply constraints, and fill pump corrective actions. Finally, it outlines a phased plan for future commissioning and experimental campaigns, including control and instrumentation shakedown, heater characterization, model calibration, and testing at state points representative of EarthEn’s TES cycle.

25 ENERGY STORAGE↗
NASA NTRS1982

Deposit formation in hydrocarbon rocket fuels with an evaluation of a propane heat transfer correlation

A high pressure fuel coking testing apparatus was designed and developed and was used to evaluate thermal decomposition limits and carbon decomposition rates in heated copper tubes for hydrocarbon fuels. A commercial propane (90% grade) and chemically pure (CP) propane were tested. Heat transfer to supercritical propane was evaluated at 136 atm, bulk fluid velocities of 6 to 30 m/s, and tube wall temperatures in the range of 422 to 811 K. A forced convection heat transfer correlation developed in a previous test effort verified a prediction of most of the experimental data within a + or - 30% range, with good agreement for the CP propane data. No significant differences were apparent in the predictions derived from the correlation when the carbon resistance was included with the film resistance. A post-test scanning electron microprobe analysis indicated occurrences of migration and interdiffusion of copper into the carbon deposit.

Masters, P. A.↗
DOE OSTI2022

Technoeconomic optimization of superalloy supercritical CO 2 microtube shell-and-tube-heat exchangers

Heat exchangers are critical components of aerospace systems and improve efficiency of operation by providing waste heat recovery. Supercritical CO has emerged as a promising candidate working fluid due to its potential in increasing the power density of heat exchangers. In this paper, a generalized costing model is developed to estimate the capital costs incurred to manufacture microtube shell-and-tube heat exchangers. This model is utilized in conjunction with an accurate and efficient 2D numerical shell-and-tube heat exchanger performance prediction model to conduct optimization studies with two key objectives – minimization of cost and maximization of heat exchanger power density – on supercritical CO microtube heat exchangers utilizing superalloy Haynes 282 as the solid material. A methodology is then demonstrated to optimize these heat exchangers using Particle Swarm Optimization for aerospace applications and highly compact and cost-effective optimal designs with power density around 20 and cost per conductance less than 5 $ ∙ K/W are obtained.

42 ENGINEERING↗
DOE OSTI2024

Blade and Rim Seal Design of a First Stage High Pressure Turbine for a 300 MWe Supercritical CO2 Power Cycle

A first stage high-pressure turbine (HPT) blade is optimized for a 300 MWe supercritical CO2 (sCO2) power cycle using the surrogate-assisted genetic algorithm optimizer in Numeca FINE/Design 3D with objectives of increasing efficiency and decreasing heat load to the blade. The National Institute of Standards and Technology Reference Fluid Thermodynamic and Transport Properties Database (NIST REFPROP) [1] data for supercritical CO2 is formatted into tables of bicubic polynomial coefficients for use in condensable gas simulations in FINE/Turbo. Nearly 3000 unique shapes are evaluated via three-dimensional Reynolds Averaged Navier Stokes simulations, yielding increases in efficiency of up to 0.85 percentage points and decreases in heat load of 14%. A final blade, deemed the advanced blade, is chosen for future experimental analysis. Following this, a squealer tip optimization is performed on both the baseline and advanced blade designs. This optimization resulted in a performance gain of 1.25 points in efficiency and 15% reduction in tip heat load compared to the baseline flat tip design at the same clearance. In tandem, an optimization of the rotor-stator platform rim seal is performed using a parametrized geometry allowing for straight, meandering, and knife seal cavities. This multi-objective optimization focuses on decreasing the cooling mass flow and increasing the heat flux from the rotor and stator disk. The optimization resulted in cooling mass flow decreases of up to 26% while maintaining the average heat flux on the rim seal.

Tuite, Logan↗
NASA NTRS2026

Hydrofluoroether (HFE) Cleaning Fluid Replacement and Qualification

This NASA Engineering and Safety Center (NESC) Technical Assessment Report addresses the urgent need to identify, test, and qualify replacement cleaning solvents and technologies following 3M’s decision to discontinue production of hydrofluoroether (HFE) products, including Novec HFE-7100, by the end of 2025. HFE-7100 is widely used across NASA for precision cleaning of ground and flight hardware, especially in oxygen system components, and as a heat transfer fluid in high-power-density thermal control systems. The assessment evaluates commercially available replacement solvents, alternative cleaning technologies, and their compatibility with NASA’s operational requirements. Key findings include the identification of viable solvent replacements, their performance in contaminant removal, materials compatibility, and oxygen system safety. The report also explores novel cleaning approaches, including aqueous, supercritical CO₂, cryogenic aerosol, plasma, UV-ozone, magnetically optimized fluids, and induced charge active filtration, highlighting their merits, limitations, and readiness for NASA adoption. The NESC provides recommendations for solvent selection, facility adaptation, and continued technology maturation to ensure mission continuity and regulatory compliance.

Alternative Cleaning Technologies↗
DOE OSTI2022

Destabilization of binary mixing layer in supercritical conditions

Compressible mixing layer instabilities are of importance to a wide range of environmental and industrial applications. Past studies have focused on either ideal-gas or real-fluid thermodynamic regimes of single-species mixing layers. However, mixing layers of binary mixtures at supercritical conditions, commonly encountered in fuel injection systems, introduce additional complexities due to the added compositional degree-of-freedom. Moreover, the effect of strong variations in thermodynamic response functions across the Widom line on the binary mixing layer stability remains poorly understood. Thus, the objective of this study is to examine the coupling between the hydrodynamic instability and the real-fluid thermodynamics across the Widom line and its effects on the overall binary mixing layer dynamics. To this end, we develop a linear stability analysis of the full binary-species compressible transport equations coupled with the PC-SAFT equation of state. Analysis shows the existence of a novel instability mechanism that arises from juxtapositioning of the Widom-line transition and the hydrodynamic inflection point. This novel thermodynamically induced instability mechanism has the net effect of destabilizing the binary mixing layer at lowering supercritical conditions towards the critical pressure point. This is in contrast to previous stability analyses of supercritical single-species mixing layers, where increasing pressure destabilizes the flow due to its effect on reducing the density stratification. The discovered thermodynamically induced instability mechanism of binary mixing flows highlights the need for an extension of classical instability criteria to incorporate the effect of strong variations in the thermodynamic response functions across the Widom line on mixing layer instability.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Supercritical CO2 Heat Pumps and Power Cycles for Concentrating Solar Power

Pumped Thermal Energy Storage (PTES) is a promising technology for electricity storage applications. An electrically driven heat pump moves energy from a cold space to a hot space, thereby creating hot and cold thermal storage. The temperature difference between the hot and cold storage is later used to drive a heat engine and return electricity to the grid. In this article, supercritical carbon dioxide (sCO2) is chosen as the working fluid for PTES, and results are compared to 'conventional' systems that use nitrogen. Molten salts are used for the hot storage which means that a CSP plant with thermal storage and an sCO2 power cycle could potentially be hybridized with PTES by the addition of a heat pump. This article describes some of the benefits of this combined system which can provide renewable power generation and energy management services. Two methods by which an sCO2 heat pump can be combined with an sCO2 power cycle for CSP are described and techno-economic results are presented. Results indicate that these systems can achieve reasonable technical performance, but that costs are currently high.

carnot battery↗
DOE OSTI2020

Supercritical CO2 Heat Pumps and Power Cycles for Concentrating Solar Power: Preprint

Pumped Thermal Energy Storage (PTES) is a promising technology for electricity storage applications. Grid electricity drives a heat pump which moves energy from a cold space to a hot space, thereby creating hot and cold thermal storage. The temperature difference between the storage is later used to drive a heat engine and return electricity to the grid. In this article, supercritical carbon dioxide (sCO2) is chosen as the working fluid for PTES, and results are compared to ‘conventional’ systems that use an ideal gas. Molten salts are used for the hot storage which means that a CSP plant with thermal storage and an sCO2 power cycle could potentially be hybridized with PTES by the addition of a heat pump. This article describes some of the benefits of this combined system which can provide renewable power generation and energy management services. Two methods by which an sCO2 heat pump can be combined with an sCO2 power cycle for CSP are described and techno-economic results are presented. Results indicate that these systems can achieve reasonable technical performance, but that costs are currently high.

41 EE - Solar Energy Technologies Office (EE-4S)↗
NASA NTRS1985

Nested subcritical flows within supercritical systems

In supercritical systems the design inlet and outlet pressures are maintained above the thermaodynamic critical pressure P sub C. Designers rely on this simple rule of thumb to circumvent problems associated with a subcritical pressure regime nested within the supercritical pressure system along with the uncertainties in heat transfer, fluid mechanics, and thermophysical property variations. The simple rule of thumb is adequate in many low-power designs but is inadequate for high-performance turbomachines and linear systems, where nested two-phase regions can exist. Examples for a free-jet expansion with backpressure greater than P sub C and a rotor (bearing) with ambient pressure greater than P sub C illustrate the existence of subcritical pressure regimes nested within supercritical systems.

Hendricks, R. C.↗
DOE OSTI2024

Summary of Structural Alloy Compatibility in Supercritical CO2 at 450°-800°C

Supercritical CO2 (sCO2) is of interest as a working fluid for several concepts including the direct- fired Allam cycle as a low-emission fossil energy power cycle. Over the past 10 years, laboratory exposures at 300 bar sCO2 have found reasonably good compatibility for Ni-based alloys at <800°C, including an assessment of the sCO2 impact on room temperature mechanical properties after 750°C exposures. However, initial screening tests at 1 and 20 bar CO2 at 900°-1100°C showed poor compatibility for Ni-based alloys. In an open cycle, the introduction of 1%O2 and 0.1- 0.25%H2O impurities at 300 bar increased the reaction rates ≥2X at 750°C. At lower temperatures, steels are susceptible to C ingress and embrittlement. Creep-strength enhanced ferritic steels may be limited to <550°C and conventional stainless steels to <600°C. Two strategies to increase those temperatures are higher Ni and Cr alloying additions and Al- or Cr-rich coatings. Alloy 709 (Fe- 20Cr-25Ni) shows some promising results at 650°C in sCO2 but reaction rates were accelerated with the addition of O2 and H2O impurities. Pack aluminized and chromized Gr.91 (Fe-9Cr-1Mo) and type 316H stainless steel show some promise at 600°-650°C but further coating optimization is needed.

Pint, Bruce↗
NASA NTRS2000

A Design Tool for Liquid Rocket Engine Injectors

A practical design tool which emphasizes the analysis of flowfields near the injector face of liquid rocket engines has been developed and used to simulate preliminary configurations of NASA's Fastrac and vortex engines. This computational design tool is sufficiently detailed to predict the interactive effects of injector element impingement angles and points and the momenta of the individual orifice flows and the combusting flow which results. In order to simulate a significant number of individual orifices, a homogeneous computational fluid dynamics model was developed. To describe sub- and supercritical liquid and vapor flows, the model utilized thermal and caloric equations of state which were valid over a wide range of pressures and temperatures. The model was constructed such that the local quality of the flow was determined directly. Since both the Fastrac and vortex engines utilize RP-1/LOX propellants, a simplified hydrocarbon combustion model was devised in order to accomplish three-dimensional, multiphase flow simulations. Such a model does not identify drops or their distribution, but it does allow the recirculating flow along the injector face and into the acoustic cavity and the film coolant flow to be accurately predicted.

Farmer, R.↗
NASA NTRS1986

The resolved layer of a collisionless, high beta, supercritical, quasi-perpendicular shock wave. III - Vlasov electrodynamics

The analysis of the fluid continuum level within the shock layer observed on November 7, 1977 by the ISEE satellites (Scudder et al., 1986) is extended to examine, within the framework of Vlasov electrodynamics, direct observational evidence for 'collisionless' resistivity. The analysis is based on the measured wave turbulence and the deviation of the observed electron velocity distribution function from the form predicted using the reversible individual electron trajectories in the presence of dc forces.

Scudder, J. D.↗
NASA NTRS1990

Re-forming supercritical quasi-parallel shocks. I - One- and two-dimensional simulations

The process of reforming supercritical quasi-parallel shocks is investigated using one-dimensional and two-dimensional hybrid (particle ion, massless fluid electron) simulations both of shocks and of simpler two-stream interactions. It is found that the supercritical quasi-parallel shock is not steady. Instread of a well-defined shock ramp between upstream and downstream states that remains at a fixed position in the flow, the ramp periodically steepens, broadens, and then reforms upstream of its former position. It is concluded that the wave generation process is localized at the shock ramp and that the reformation process proceeds in the absence of upstream perturbations intersecting the shock.

Thomas, V. A.↗
NASA NTRS2001

High Pressure, Transport Properties of Fluids: Theory and Data from Levitated Fluid-Drops at Combustion-Relevant Temperatures

The objective of this investigation is to derive a set of consistent mixing rules for calculating diffusivities and thermal diffusion factors over a thermodynamic regime encompassing the subcritical and supercritical ranges. These should serve for modeling purposes, and therefore for accurate simulations of high pressure phenomena such as fluid disintegration, turbulent flows and sprays. A particular consequence of this work will be the determination of effective Lewis numbers for supercritical conditions, thus enabling the examination of the relative importance of heat and mass transfer at supercritical pressures.

Bellan, J.↗
DOE OSTI2025

Computational and Experimental Investigation of Discrete “W” Turbulators for sCO2 Turbine Internal Cooling

Direct-fired supercritical CO2 (sCO2 ) cycles are of particular interest for power generation due to the potential for higher thermal efficiencies with inherent CO2 capture. Direct fired sCO2 turbines must withstand high temperatures and the density of the working fluid is much higher than conventional Brayton cycles. Based on conventional Brayton cycle applications, internal serpentine cooling channels with ribbed turbulator strips are a common approach to achieve the required cooling, while minimizing coolant utilization. Most of the previous studies of coolant channel heat transfer enhancements have focused on serpentine channels using air as the cooling media at Reynold’s numbers typical of Brayton cycles. This paper investigates the Nusselt number augmentation of coolant channels with no features, ribbed turbulators, and discrete “W” turbulators with surface roughness effects included and CO2 as the coolant. The numerical results are compared to experimental results using CO2 as the cooling media at Reynold’s numbers ranging from 100,000 to 300,000. The results show the Nusselt number augmentation plateaus with increasing Reynolds number, in contrast to the decay observed in prior publications with air as the coolant media. Additionally, the CFD results indicate the discrete “W” geometry provides a 10% increase in Nusselt number augmentation relative to the angled ribbed turbulators.

computational fluid dynamics (CFD)↗
DOE OSTI2022

Modeling of Supercritical CO2 Shell-and-Tube Heat Exchangers Under Extreme Conditions. Part I: Correlation Development

Abstract High-temperature supercritical CO2 Brayton cycles are promising possibilities for future stationary power generation and hybrid electric propulsion applications. Heat exchangers are critical components in supercritical CO2 thermal cycles and require accurate correlations and comprehensive performance modeling under extreme temperatures and pressures. In this paper (Part I), new Colburn and friction factor correlations are developed to quantify shell-side heat transfer and friction characteristics of flow within heat exchangers in the shell-and-tube configuration. Using experimental and computational fluid dynamics (CFD) data sets from existing literature, multivariate regression analysis is conducted to achieve correlations that capture the effect of multiple critical geometric parameters. These correlations offer superior accuracy and versatility as compared to previous studies and predict the thermohydraulic performance of about 90% of the existing experimental and CFD data within ±15%. Supplementary thermohydraulic performance data are acquired from CFD simulations with supercritical CO2 as working fluid to validate the developed correlations and demonstrate its capability to be applied to supercrtical CO2 heat exchangers.

Engineering↗